Pickling-bath and method of making the same.



DISON F. HOFFMAN, 0F PITTSBURGH, PE

WILLIAM M. PARKIN, OF PI NNSYLVANIA, ASSIGNOR 0F oNE-HALF TO T'ISBURGH, PENNSYLVANIA.

PICKLING-IBATH AND METHOD OF MAKING THE SAME.

No Drawing.

To all whom it may concern:

Be it known that I, ADDISON F.-HOFFMAN, a citizen of the United States, residing at Pittsburgh, in the county of Allegheny and .State of Pennsylvania, have invented certain new and useful Improvements in Pickling- Baths and Methods of Making the Same, of which the following is a specification'.

This invention relates to pickling baths and methods of making the same and utilizing the waste contents thereof, pertaining more particularly to baths adaptedto pickle iron and steel, although the bath may be employed for the treatment ipf copper materials.

Pickling baths heretofore commonly employed have generally consisted of a solution of sulfuric acid (H 80 or hydro-chloric or muriatic acid (H01).

In the sulfuric acid bath, the action is principally by dissolving the metal back of the scale or oxid films which form over the metal causing the scale or film to fall off. Some of the scale is also dissolved by the hot sulfuric acid solution producing ferric sulfate which also has a pickling value, one third of its acid radical being still available for pickling purposes. The action on the oxid scale is not, however, as active as where muriatic acid solution or one of acid sodium sulfate (NaHSOQ is used, the latter having, in some instances, been used for pickling purposes. The reactions with a sulfuric acid pickling solution are substantially as follows:

and

this and other reasons, among which is the question of economy, the use of strong sul-, furic acid solutions for pickling purposesis decreasing at the present day excepting Specification of Lettegs Patent. Application filed July 24, 1915.

Patented May 115, 1917. serial No. 41,690.

where the material is oxids.

The inuriatic acid bath is more generally used, it acting somewhat differently in the pickling operation, tending more to dissolve the scale or oxid, and dissolving a very much less amount of metal than the sulfuric bath, producing an increase in finished material output, with a surface condition of the metal equally satisfactory. One of the reasons for this more extensive use is the lower cost of the acid, it being possible to produce it at very low prices.

The useof acidsodium sulfate has also been contemplated, this being the by-prodnot from the manufacture of sulfuric and nitric acids. It has an action somewhat similar to the muriatic acid and has several advantages over the use of sulfuric acid.

The present practice in connection with pickling baths is to discharge the spent waste liquor from the bath into streams or on to the ground where it may reach streams, the result being that the stream is contaminated, making it injurious not only to fish life, but detrimental to human beings; in addition, it causes an enormous industrial damage. This fact has led to attempts to prevent such stream contamination.

While it is possible to reclaim some of the elements of the liquor in the form of byheavily incrusted with products, these attempts have not had material application through various causes, among which is the cost of the operation. The extensive demand for sulfate of iron or copperas (FeSOQ liquor of sulfuric ables the liquor to be utilized in the production of this sulfate, tends to reduce the effects of stream contamination by this form of waste liquor, but the increase in the use of pickling solutions in recent years has more than offset the demand for the sulfate, so that an excess of the liquor has been produced, which excess still provides such source of contamination.- v The present invention aims more particularly to eliminate these difliculties b the formation of a pickling solution which is not only more effectivethan either of the baths referred to, but, in addition, is of relatively lower cost and isrenewable,'thus eliminating the presence of spent or waste liquor, the bath providing a removable precipitate.

, acomponent of the waste acid baths and which ericondition by-the from which the cost The remaining solution is retained in active addition of the compounds bath is formed. The precipitate can be treated to produce the acids, thus reclaiming elements which enter into the bath formation. The cost of operation when the pickling solution of the present invention is employed is greatly reduced, approximating one-half the cost under present methods, and where the reclamation is had, the cost of the entire operation is approximately one-fourth to one-third of the where the sulfuric acid bath is employed.

The solution forming the bath of the present lHVGIItlOII lS'PIOVIdBd by running into the pickling tank or vat a concentrated solution of salt water, either hot or cold, from one tank, and sulfuric acid from another tank. The chemical reaction which takes place in the pickling tank due to the union of these two compounds is as follows:

these substances being employed in the proportion of their molecular weights, the su may also be the protoxid' ply being controlled by means of valves, t e quantity of each required being dependent upon the strength of the solution, the quantity of metal pickled, and the quantity of each required to satisfy the chemical equations. Salt could be added to the sulfuric acid solution, but saltwater has several advantages.- This results in the formation of a solution of acid sodium sulfate and hydrochloric acid, each of which is capable of independent use as a pickling solution, the solution formed being one which is a combination of these independent pickling solutions, causing the bath to be more active than with either separately, and obviating the production of poisonous hydrogen gas. H 80.

used in excess.

The muriatic or hydrochloric acid produced by this reaction, in the presence of an abundance of water, remains in solution instead of being driven off as would be the case.

where the sulfuric acid was poured upon salt. The acid sodium sulfate also remains in solution.

The bath works best when boiling hot. When the pickling operation takes place in connection with iron or steel, the following approximate reactions occur:

These reactions are only illustrative, as the scale. on iron andv steel is not strictly ferric oxid (Fe O but a combination of this with (FeO) and the ferroso-ferric oxid (Fe O,) in variant proportions; to show the complete effect, the chemical equations would have to be adjusted tosuit the other. oxids.

The effect of this bath, in practice, is however, to clean the metallic surface free from scale completely, rapidly, and economically, dissolving only about one-third of the quantity of metal dissolved by a sulfuric acid picklin solution, and is considerably more profita le.

The quantity of pickling liquor formed is under direct control, so that the bath can always be kept of the desired strength. The water required to replace that evaporated can be supplied through the salt solution or" by blowing steam into the vat, the

latter also keeping up the heat. The greater v part of the heat, however, is supplied through the hot material pickled.

The chlorid of iron (ferrous chlorid- FeCl the sulfate of iron (ferrous sulfate- FeSOQ, and the sulfate of soda (sodium sulfateNa,S.O which are produced as a result of the reactions, precipitate to the bottom of the tank, probably partly as double salts, when the solution becomes sufliciently concentrated, forming a cake which can be readily removed when desired by means of a suitable rake.

It is not necessary to discharge this pickling solution at intervals, but only to keep it hot, add the necessary chemicals and remove the crystalline mass from the bottom of the tank at intervals, the solution not becoming spent but remaining active for pickling purposes by this treatment.

The crystalline waste thus produced can be treated to form a stimulant fertilizer, gas purifying material, pigment, or be sold as a weed killer.

This waste can also be treated to provide a regenerative action in the production of acids for use in the bath, thus reducing the cost of operation. This action may be provided by a heating or roasting action, em-

, ploying a retort and a heat ranging from 700to 900 0., the retort having pipe connection with the pickling tank or a separate tank containing water. Under the heating action, the crystalline waste is separated into oxids and gases, the approximate reactions being as follows:

The gases, upon reaching the water of the pickling tank or separate tank, form sulfuric and hydrochloric acids, both of which may be used in the formation of the liquor. The V somewhat refractory sulfate of soda can be decomposed in the retort at comparatively low temperatures by the additionof a little sand or other form of silicate.

In this manner, more than half of the acids can be recovered for further use, thus reducing the amount of chemicals required, obviously reducing the cost of the pickling.

The oXid residue recovered from the re- 3. A pickling bath substantially nonwasting in character and composed of a solution having not less than two acid pickling elements adapted to form precipitates in the presence of the material being pickled, the non-precipitate having the property of continued activity upon the addition of the element-producing chemicals.

4. A pickling bath substantially nonwasting in character and composed of a solution having "not less .than two pickling elements adapted to form precipitates in the presence of the material being pickled, the precipitates, under the action of heat, forming gases combinable, with the nonprecipitate' of the solution to ling elements.

5. The method of producing a pickling bath which consists in combining not less than two pickling elements in an abundance I of water, forming precipitates by the presence of the material being pickled, re-

moving the precipitates and heating them to form gases combinable with the nonprecipitate of the solution to produce pickling elements. I

' 6. The method of producing a pickling bath which consistsin combining not less than two picking elements in an abundance of water, forming precipitates by the presence of the material being pickled, removing the precipitates and heating them to decompose gases combinable' with water to produce pickling elements.

7. The method of pickling iron or steel produce pickwhich consists in subjecting the material to be pickled to the action of a pickling bath containing acid sodium sulfate and hydrochloric acid in solution, whereby precipitation will be provided, and renewing the activity of the bath by the addition of the chemical sources of said pickling elements. '8. The method of pickling iron' or steel which consists in subjecting the material to be pickled to the action of a pickling bath containing acid sodium sulfate and hydro.- chloric acid in solution, whereby precipitation will be provided, removing the precipitate, and renewing the activity of the bath by the addition of the chemical sources of said pickling elements.

9. The method of pickling iron or steel which consists in subjecting the material to be pickled to the action of a pickling bath containing acid sodium sulfate and hydrochloric acid in solution, whereby precipitation will. be provided, and renewing the activity of the bath by the addition of the chemical sources of said pickling elements in regulated quantities.

10. The method of pickling iron or steel which consists in subjecting the material to be pickled to the action of a pickling bath formed from regulated quantities of sulfuric acid and of a concentrated solution of salt water in proportions to substantially eliminate free sulfuric acid in the bath whereby precipitation will be provided, and renewing theactivity of the bath by the addition of regulated quantities of the sulfuric acid and salt water solution.

11. The method of pickling iron or steel which consists in subjecting the material to be pickled to the action of a pickling bath formed from regulated quantities of sulfuric acid and of a concentrated solution of salt water in proportions to substantially eliminate free sulfuric acid in the bath, whereby precipitation will be provided, removing the precipitate, and renewin the activity of the bath by the addition 0 regulated quantities of the sulfuric acid and salt water solution.

12. The method of pickling iron or steel which consists in subjecting the material to be pickled to the action of a pickling bath having the property of producing precipitates of sodium sulfate, ferroussulfate, and ferrous chlorid in the presence of the material being pickled.

In testimony whereof I aflix my signature in presence of two witnesses. ADDISON F. HOFFMAN.

Witnesses:

MARY MCLAUGHLIN,

' W. G. Doommn' 

